downpipe, check engine light Options

[dsmwanabe]

ok My questions are. I am going to be putting my new Big T 28 on this weekend and my three inch downpipe on my 98 gsx . Now I know that sence the new downpipe takes the place of the cat that I will get a check engine light. S0 I heard of a bypass thing that can be done with a little bit of work to it. First is this really safe. I won't have the computer reading false readings from the other o2. that may make the engine run like crap. Does it just trick the com into thinking that its all A O K for all problems. what are the pros and cons to doing this bypass. Also I don't want a dumb answer like just take out the light for the CEL. I like haveing that litle guy working just right, now that I am starting to bolt on some real HP gainers I want that little safty net no matter how smallit is.
Please if you could explain it to me what it is that the bypass does and why its safe or unsafe I would really like to know, because cutting 16 inches out of the downpipe and having to find someone with a tig welder and who knows how to weld stainless steal is not an option

[99Spyder]

I can't say exactly what the electrical components are doing except that I am sure the capacitors are sending a consistent stoichiometric signal (ideal air/fuel ratio). This would ensure that no fuel trims are being utilized due to a wacky signal from O2 #2. The resistor on the black wires adds 12 Ohms of resistance to give the impression that the heating element is in use.

[doayamaha]

i have heard that in some cases you can just loop the two wires, i haven't done it but i have heard that it works

[AWD DSM 1]

From my understanding, the main function of the rear o2 sensor is to make sure the cat is working correctly. All the air/fuel ratio info for the motor is taken off the front o2. By re-wiring the rear, your simply tricking the ECU into thinking that the cat is still there and working normally. All other functions should still work.

Your best bet is still to get a Datalogger so you can see yourself what the car is doing, and not have to rely on the appropriately named "dummy" lights. Usually when they go on it's too late.

[ncgalant]

I have heard several accounts of people leaving the rear O2 hooked up and just hanging there with no CEL. You might want to try that first. I ran with no rear O2 at all for a year with no problems other than the CEL being on. Like AWD said, it is only a check for your cat. Your gas milage and drivablility won't change.

[dsmwanabe]

thanks for all the good info i will try the not doing anything to it first then I think I will get the bypass a little later. Thanks again

[MaxOvrDrv]

Could you post a link to the Bypass that you are talking about. I would like to do it on my car as well. thanks ]

Jeff